The preparation of rigid cross-linked polyurethane foams, polyisocyanurate foams and polyurethane foams which are free of disubstituted ureas that describe the addition of an alkylene carbonate is known.
U.S. Pat. No. 3,751,392 describes a process for the preparation of a polyurethane foam, which is essentially free of disubstituted ureas, employing as the blowing agent an inorganic hydrated metal salt and as heavy metal carboxylate catalyst with the addition of organic carbonates as liquid modifiers.
U.S. Pat. No. 4,033,908 relates to the preparation of a polyisocyanurate by reacting a polyisocyanate in the presence of a blowing agent and a trimerization catalyst with the addition of a plasticizing amount of a nonreactive liquid organic carbonate to improve friability and dimensional stability properties of the foam.
U.S. Pat. No. 4,071,482 describes a highly flame-resistant rigid polyurethane foam having improved friability which is the reaction product of a halogenated polyether polyol having a hydroxyl number of about 300 to 600 and a functionality of 3 to 8 and a polyisocyanate in the presence of a catalyst and a blowing agent, with the foam containing from 1 to 10% by weight of a liquid alkylene carbonate.